The invention relates generally to water pumps and more specifically to a water pump driven by a viscous coupling.
Water pumps are typically used on vehicles today to provide heat transfer means for an engine during operation. The engine crankshaft typically drives water pumps at a fixed ratio. Thus, as the engine idle speed is reduced, as is the trend in vehicles today to reduce emissions, the water pump speed is correspondingly reduced. This reduction in water pump speed results in a reduction in the coolant flow through the cooling system which can result in poor heater output for the interior of the vehicle when needed in cold weather and also can result in poor coolant flow for engine cooling during hot weather.
Increasing the water pump speed by increasing the drive ratio from the crankshaft will increase the coolant flow at engine idle speeds, but it may result in overspeeding the pump at higher engine speeds which may produce pump cavitation and reduced water pump bearing life. Pump cavitation can result in pump damage and a reduction in cooling system performance. current state of the art is to add an auxiliary water pump, typically electrically driven, to provide additional coolant flow at low engine idle speeds. Another approach is to use moveable vanes in the inlet of the water pump to throttle the coolant flow at higher engine speeds.
It is thus an object of the present invention to provide good coolant flow at low engine idle speeds while avoiding pump cavitation at higher engine speeds without the need for an auxiliary water pump or moveable vanes.
The above and other objects of the invention are met by the present invention that is an improvement over known water pumps.
The present invention provides a viscous coupling, or clutch, positioned on the input shaft of the water pump. At engine idle or low speeds, wherein the water pump is driven at very close speeds to the input speed, the viscous coupling has minimal effect on the speed of the pump. However, due to the presence of the viscous coupling, a larger water pump may be used, resulting in good coolant flow at engine idle or lower speeds.
As engine speeds are increased, the viscous coupling slips, resulting in lower input speeds for the water pump, thereby reducing the risk of pump cavitation. This may also increase the life of the water pump bearing.
In an alternative preferred embodiment, the body of the viscous coupling can be designed to be immersed in engine coolant, which would enhance the removal of heat due to slip from the viscous coupling at high speed slip conditions.
Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.